For a number of known reasons, spinal fixation devices are used in orthopedic surgery to align and/or fix a desired relationship between adjacent vertebral bodies. Such devices typically include a spinal fixation element, such as a relatively rigid fixation rod, that is coupled to adjacent vertebrae by attaching the element to various anchoring devices, such as hooks, bolts, wires, or screws. The fixation elements can have a predetermined contour that has been designed according to the properties of the target implantation site, and once installed, the instrument holds the vertebrae in a desired spatial relationship, either until desired healing or spinal fusion has taken place, or for some longer period of time.
Spinal fixation elements can be anchored to specific portions of the vertebrae. Since each vertebra varies in shape and size, a variety of anchoring devices have been developed to facilitate engagement of a particular portion of the bone. Pedicle screw assemblies, for example, have a shape and size that is configured to engage pedicle bone. Such screws typically include a threaded shank that is adapted to be threaded into a vertebra, and a head portion having a rod-receiving element, usually in the form of a U-shaped slot formed in the head. A set-screw, plug, or similar type of fastening mechanism is used to lock the fixation element, e.g. a rod, into the rod-receiving head of the pedicle screw. In use, the shank portion of each screw is threaded into a vertebra, and once properly positioned, a rod is seated through the rod-receiving member of each screw and the rod is locked in place by tightening a cap or other fastener mechanism to securely interconnect each screw and the fixation rod.
Recently, the trend in spinal surgery has been moving toward providing minimally invasive elements and methods for implanting spinal fixation devices. For example, one such method, a rod-first method, includes inserting a spinal rod through a first incision and positioning the spinal rod along a patient's spinal column adjacent to one or more vertebra. After the spinal rod is inserted, a first bone anchor is inserted through the first bone anchor incision or through a separate incision, and then additional bone anchors are inserted each through a separate incision along the spinal rod. After a bone anchor is inserted and anchored in bone it is coupled to the spinal rod. A rod-first method is a minimally invasive technique in which the bone anchors are inserted after the rod and adjacent to the rod, as opposed to a conventional surgical technique in which the bone anchors are inserted first then the rod is placed in rod-receiving elements lying over the heads of the bone anchors.
However, such minimally invasive procedures, such as rod first techniques, introduce other issues. Because the bone anchors are inserted percutaneously after the spinal fixation element and adjacent to the spinal fixation element, connecting the bone anchors to the spinal fixation element can be difficult because the surrounding tissue and muscle may obstruct a direct view of the surgical site. Thus, what is needed when using minimally invasive surgical procedures, such as rod first techniques is a means for being able to engage a previously inserted spinal fixation element with an implant at a sub facial surgical site.